Lubricant base stocks are commonly used for the production of lubricants, such as lubricating oils for automotives, industrial lubricants and lubricating greases. A base oil is defined as a combination of two or more base stocks used to make a lubricant composition. They are also used as process oils, white oils, metal working oils and heat transfer fluids. Finished lubricants consist of two general components, lubricating base stock and additives. Lubricating base stock is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base stocks are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base stocks and individual additives.
According to the American Petroleum institute (API) classifications, base stocks are categorized in five groups based on their saturated hydrocarbon content, sulfur level, and viscosity index (Table 1). Lube base stocks are typically produced in large scale from non-renewable petroleum sources. Group I, II, and III base stocks are all derived from crude oil via extensive processing, such as solvent extraction, solvent or catalytic dewaxing, and hydroisomerization. Group III base stocks can also be produced from synthetic hydrocarbon liquids obtained from natural gas, coal or other fossil resources. Group IV base stocks, the polyalphaolefins (PAO), are produced by oligomerization of alpha olefins, such as 1-decene. Group V base stocks include everything that does not belong to Groups I-IV, such as naphthenics, polyalkylene glycols (PAG), and esters.
TABLE 1APIclassificationGroup IGroup IIGroup IIIGroup IVGroup V% Saturates<90≧90≧90Polyalpha-All others% S>0.03≦0.03≦0.03olefinsnotViscosity80-12080-120≧120(PAO)belonging toIndex (VI)group I-IV
The automotive industry has been using lubricants and thus base stocks with improved technical properties for a long time. Increasingly, the specifications for finished lubricants require products with excellent low temperature properties, high oxidation stability, low filterability and low volatility. Generally lubricating base stocks are base stocks having kinematic viscosity of about 3 cSt or greater at 100° C. (Kv100); pour point (PP) of about −12° C. or less; and viscosity index (VI) about 90 or greater. In general, high performance lubricating base stocks should have a Noack volatility no greater than current conventional Group I or Group II light neutral oils. Currently, only a small fraction of the base stocks manufactured today are able to meet these demanding specifications.
U.S. Patent Publication No. 2006/0019841 A1 discloses the use of a C12-20 polyalkyl methacrylate polymer as a lubricating oil additive such that the C12-20 polyalkyl methacrylate polymer accounts for 0.1 to 0.3% by weight of the finished lubricating oil. The use comprises the addition of said C12-20 polyalkyl methacrylate polymer to a lubricating oil based on mineral oil to improve the filtration of said lubricating oil based on mineral oil.
Group I base stocks may be further broken down based on kinematic viscosity range at 100 deg. C. into light neutral (LN), heavy neutral (HN) and bright stock (BS). Light neutral has a kinematic viscosity in the range of 4-6 cSt, heavy neutral (HN) has a kinematic viscosity in the range of 10-12 cSt, and bright stock has a kinematic viscosity in the range of 30-34 cSt. Due to its high viscosity, bright stock is used in many industrial oil applications. In many of these applications, cleanliness of the lubricating oil is an important property because the oil may pass through fine orifices and filters. The lubricating oil needs to have acceptable filterability to keep fine orifices and filters from plugging up during operation. Bright stock is produced commercially with a wide range of filterabilities. Bright stock presents challenges for filterability because of its relatively high viscosity. In addition, filterability becomes more of an issue as bright stock is produced from more challenged crudes.
Hence, there is a need to improve the filterability of bright stock to increase the range of crude oils that it may be produced from and the lubricating oil applications that it may be used in.